In accordance with recent developments of higher integration of semiconductor devices, mass production of LSI with a design rule of about 0.20 μm has already started and mass production of LSIs with a design rule of about 0.15 μm will be realized in the near future.
In addition, a chemical amplification type positive resist composition is superior in resolution and sensitivity to a conventional non-chemical amplification type positive resist composition using a novolak resin as a base resin and a naphthoquinonediazide sulfonate ester as a photosensitive agent. Therefore, the conventional non-chemical amplification type positive resist composition has recently been replaced by the chemical amplification type positive resist composition.
At present, it is popular to employ chemical amplification type positive resist compositions which use, as a base resin, a copolymer or mixed resin, wherein an acetal group, which is dissociated with a comparatively weak acid, and an acid-dissociable group such as tert-butoxycarbonyl group, tert-butyl group or tetrahydropyranyl group, which is not easily dissociated with a weak acid but is dissociated with a strong acid, coexist and also use a sulfonyldiazomethane acid generating agent as an acid generating agent (Japanese Patent Application, First Publication No. Hei 8-15864, Japanese Patent Application, First Publication No. Hei 8-262721, Japanese Patent Application, First Publication No. Hei 9-160246, Japanese Patent Application, First Publication No. Hei 9-211868, Japanese Patent Application, First Publication No. Hei 9-274320 and Japanese Patent Application, First Publication No. Hei 9-311452).
As prior art known before the above techniques are laid open to public, for example, there are those using a copolymer of p-(1-ethoxyethoxy) styrene and p-hydroxystyrene as a base resin and a sulfonyldiazomethane acid generating agent such as bis (cyclohexylsulfonyl) diazomethane as an acid generating agent (Japanese Patent Application, First Publication No. Hei 5-249682). Such a resist composition containing a combination of an acetal (alkoxy-alkyl) group, which is dissociated with a comparatively weak acid, as a dissolution inhibiting group and a sulfonyldiazomethane compound capable of generating a weak acid forms a resist pattern having high resolution. However, the resist pattern formed from the resist composition tends to narrow over time and are not satisfactory because of insufficient heat resistance and dependence on a substrate. Therefore, as described above, there was proposed a technique whose drawbacks were solved by the base resin wherein the acetal group, which is dissociated with the comparatively weak acid, and the acid-dissociable group, which is dissociated with the strong acid, coexist.
With improvements in semiconductor devices, a conventional method of forming Al wiring using a reactive ion etching (RIE) technique is already being replaced by a method of forming Al.Cu wiring or Cu wiring using a damascene technique in the semiconductor device manufacturing process.
It is expected that the damascene method will become popular in the process for manufacturing semiconductors of the next generation or the subsequent generation.
In the damascene technique, a method of forming two kinds of portions to be etched such as via holes and wiring grooves is referred to as a dual damascene method.
In the dual damascene method, two kinds of a trench-first technique of previously forming wiring grooves and a via-first technique of previously forming via holes exist (“Latest Developments in Cu Wiring Techniques”, pages 202 to 205, May 30, 1998, published by Realize Co., Ltd., edited by Katsuro FUKAMI).
In the via-first method of manufacturing semiconductor devices, for example, a base material obtained by laminating a first interlaminar insulating layer, an etching stopper layer and a second interlaminar insulating layer in order on a substrate is prepared. Then, a chemical amplification type positive resist composition is applied on the base material and the coated base material is subjected to exposure in accordance with a predetermined pattern, thereby to make the exposed portion alkali-soluble. The exposed portion is removed with an alkali developing solution and the lower layer with no resist pattern is etched to form via holes which penetrate the first interlaminar insulating layer, the etching stopper layer and the second interlaminar insulating layer. Then, the chemical amplification type positive resist composition is further applied and the coated one is subjected to exposure, thereby to make the exposed portion alkali-soluble. The exposed portion is removed with an alkali developing solution and the lower layer with no resist pattern is etched to widen the groove width of the via holes formed on the second interlaminar insulating layer, thereby to form wiring grooves. Finally, copper, or copper and aluminum are embedded in via holes formed on the first interlaminar insulating layer and the etching stopper layer as well as wiring grooves formed in the second interlaminar insulating layer thereon, thereby to complete wiring having generally T-shaped cross sectional profile.
However, the via-first dual damascene method of forming wiring grooves after forming via holes had a drawback that resist residue is likely to be produced in the vicinity of the upper portion (the bottom portion of wiring grooves of the second interlaminar insulating layer) of via holes as a result of poor development when a resist pattern is formed using the above chemical amplification type positive resist composition using a base resin wherein an acid-dissociable dissolution inhibiting group, which is easily dissociated with a comparatively weak acid, and an acid-dissociable dissolution inhibiting group, which is not easily dissociated with a weak acid but is dissociated with a strong acid, coexist. As a result, there arises a problem that an expected fine pattern cannot be formed.